I have the same radiator, sounds like a 46 to me.
The top is all brass and the fittings are cast on my'n. I have to have mine rebuilt so it can take the pressure of a 350. The top filler cap is about 3 inches in diameter and it sits on a cast elbow so I'm thinking it might have came out of a cabover but it is a 46. Picked it up for 50 buck in Winnipeg Canada, nothing really wrong with it.
Bob T